1. Field of the Invention
The present invention relates to a technique for printing images by forming dots on a printing medium during main scanning, and more particularly to a technique for adjusting misalignments of recording positions in the main scanning direction to improve quality of printed images.
2. Description of the Related Art
Recently, printing apparatuses that print images by ejecting ink droplets to form ink dots on a printing medium are widely used as output devices of images. Hereinafter, such printing apparatus will be referred to as ink jet printing apparatus. A print head of the ink jet printing apparatus is provided with a plurality of nozzle groups for respective color inks, and the ink jet printing apparatus prints images by ejecting ink from each nozzle onto the printing medium to form ink dots on the printing medium. These printing apparatuses often perform bi-directional printing in which ink dots are formed on not only forward passes but also backward passes of main scanning while the print head is reciprocating relative to the printing medium, to achieve higher printing speed. In the case of bi-directional printing, an adjustment process for reducing misalignments of dot forming positions is performed by setting a position adjustment value for adjusting misalignments of ink dot forming positions on forward passes and backward passes in order to improve picture quality (e.g. JAPANESE PATENT LAID-OPEN GAZETTE No. 11-286142).
Some recent printing apparatuses can change the type of ink ejected by each nozzle group to perform a variety of bi-directional printings having different characteristics of print performance such as quality-conscious bi-directional printing and speed-conscious bi-directional printing according to the situation of the printing. However, changing ink types may vary the ink type whose misalignments of dot forming positions tend to be conspicuous. Therefore, even if the forming positions of ink dots are adjusted based on the identical position adjustment value, dots formed by a nozzle group, whose misalignments were inconspicuous before the change of inks, may become conspicuous due to the change of inks, which prevents improved picture quality.